Evaporative and regenerative waste water incineration system

ABSTRACT

There are provided an evaporative/regenerative incineration system for organic waste water for incinerating organic waste water and volatile organic compounds completely at low expenses and a method therefor. Waste gas is generated by evaporating waste water including organic compounds in an evaporator and the generated waste gas is mixed with air in a regenerative thermal oxidizer (RTO) in flow communication with the evaporator for oxidation. The heat energy generated from the oxidation is collected and supplied to the evaporator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system for incinerating organic wastewater and volatile organic compounds and a method therefor and moreparticularly, an evaporative and regenerative waste water incinerationsystem for economically and efficiently removing the organic compoundsby oxidizing the waste gas generated from evaporated waste waterincluding the organic compounds using a regenerative thermal oxidizer.

2. Description of the Related Art

Generally, volatile organic compounds including a total of hydrocarboncompounds are materials generally created in chemical factories, wastewater treatment plants and during the printing works in carmanufacturing factories, and cause the photochemical smog, warming ofthe Earth, destruction of ozone layer in the stratosphere, and so on,and very fatally toxic to human body such as developing cancer, etc. andthe human environment.

The known techniques to treat the volatile organic compounds areincineration, absorption for removal, adsorption, cooling condensation,biological treatment and layer separation methods, etc. And especiallyregenerative thermal oxidation method is widely used.

A Regenerative thermal Oxidizer (now referred to as RTO) is operated byincinerating the waste gas including the volatile organic compounds, andcollecting the heat generated during the incineration through a ceramicfiller material thereby greatly reducing the operation expenses of thesystem, and minimizing an installation space. The treatment efficiencyof the RTO is very high over 99%, and a second contamination is little,and if the concentration of the volatile organic compounds in the wastegas is over 300 vppm, a supplementary supply of energy is not necessaryby using the incineration energy from the system, itself.

Describing its operation more detail, the RTO maximmably collects thewaste heat energy discharged from the waste gas and turns the energy topreheat introduced gas. For this purpose, it employs ceramic which isdirectly heated and cooled for its regeneration instead of a typicalheat exchanger.

That is, when using a shell & tube type heat exchanger or a plate typeheat exchanger for the heat exchange of gas, the temperature differenceof the gas between the inlet and the outlet of the heat exchanger is 100to 200° C. thereby limiting the usage. However, the ceramic has itsmaximum service temperature by 950° C., and when regenerating, thetemperature difference between the inlet and the outlet can be reducedto 20° C. thereby achieving 98% of the heat recovery rate.

FIGS. 1 and 2 show the operation states of forward/rearward direction inthe typical RTO. After heating a furnace placed between ceramic layers1, 2 disposed on the left and right sides of the RTO to be appropriatefor the operation of the furnace at the start of the operation, thewaste gas is introduced.

The waste gas is preheated up to the temperature of the furnace passingthe ceramic layer 1, and the organic gas in the waste gas starts itsoxidation and while passing through the furnace for a certain timeperiod, all the organic compounds are oxidized at a temperature of about800° C.

At this time, while the treated gas at a high temperature passes thoughthe ceramic layer 2, the gas discharges out almost all heat so that thegas is cooled just down to a temperature of 10 to 30° C. higher than thetemperature of the inlet in the ceramic layer 1.

At this time, after a while, the inlet path for the gas is switched asshown in FIG. 2.

The switching operation shown in FIGS. 1 and 2 is repeated with acertain interval of time (about 1.5 to 3 minutes) thereby minimizing theenergy for the gas incineration.

The system shown in FIGS. 1 and 2 is called a 2-bed type RTO, and the2-bed type RTO is an economical system. However, not-treated gasexisting on the ceramics of the RTO during the switching of the valvesand other not-treated gas passing through the furnace of the RTO in aroundabout way are discharged at a time during the switching of thevalves so that the removal efficiency of the whole organic compounds isaround 95% due to the discharge of the not-treated gas.

To address this problem, a 3-bed type RTO or a gas buffer can be used.The case of using the buffer is shown in FIG. 3.

That is, the incineration system comprises an RTO, a gas buffer and ablower.

The operation of forward direction by using the buffer 12 is describedas follows:

The not-treated waste gas from the processes is introduced into aceramic layer 3 on one side of the 2-bed type RTO with a valve 5 open.The introduced gas at room temperature is heated up to 800° C. foroxidation by the regenerative ceramic so that the organic volatilecompounds (VOC) in the air is oxidized. The temperature of the gas afteroxidation is about 830° C. which is 30° C. higher than that of theregeneration ceramic. The gas at this temperature is cooled down passingthrough a ceramic layer 4 at the other side. Most of the heat istransmitted to the ceramic layer 4 thereby increasing the temperature ofthe ceramic 4. The cooled-down gas passes through a valve 8, the blower13, and a valve 10 in turn and is discharged to the atmosphere.

As described above, during the operation of the forward direction, thevalve 5, 8 are open and the valves 6, 7 are closed. A buffer valve 9 atthe front of the gas buffer is closed.

While the operation of the forward direction is maintained for about 2minutes, the ceramic of the ceramic layer 3 preheats the gas and iscooled down. The ceramic layer 4 absorbs the heat of the heated gas andis heated. At this time, the introduction of the gas is started with theoperation start of the rearward direction.

The operation conditions in the forward direction and the rearwarddirection are the same, and the introduction direction of the waste gasis changed to the ceramic layer 4 on the other side. There exists aswitching time between the operation of the forward/rearward direction.

Since the valves 5,8 of the rearward direction are closed and the valves6,7 are open, not-treated waste gas present between the ceramic layer 3and the valve 5 passes through the valve 7 by the blower 13, and isdischarged through the valve 10 to the atmosphere.

To prevent this, by using the gas buffer 12, the buffer valve 9 is open,and the valve 10 of a pipe leading to a smokestack is closed.

Therefore, the not-treated gas is collected into the gas buffer 12through the buffer valve 9, and the treated gas on the upper side of thegas buffer 12 is directly discharged out of the smokestack.

After the switching time, the gas path at the back side of the RTO isturned to the discharge pipe, and the buffer valve 9 is closed.

There is provided a diaphragm inside the gas buffer 12 to minimize themixing of the introduced gas. The lower side of the buffer is connectedto the inlet line for not-treated gas, and the upper side of the bufferis in flow communication with the discharge pipe to the atmosphere. Thenot-treated gas stored in the buffer is automatically circulated to thefront of the RTO with the valve 11 open, and the inside of the buffer ischanged with a gas introduced from the atmosphere until the nextswitching time.

Meanwhile, in chemical factories, the waste water treatment and carsmanufacturing companies, large amount of other kinds of waste waterbeside the above organic compounds is generated. When the concentrationof the organic compounds in the organic waste wate is low (e.g., CODlower than 5,000 ppm), it is treated with active oil treatment, but incase of high concentration (e.g., COD higher than 10,000 ppm), theactive oil treatment is not sufficient and not economical so that it istreated by incinerating.

At this time, the waste water incineration using a typical incinerationfurnace is operated by introducing the waste water including organiccompounds (VOC included) into the incineration furnace, and oxidizingthe organic compounds in the waste water by heating the waste water upto 950° C. However, even though the heat exchanger can be used tocollect the energy, the recovery rate of the heat is very low and theoperation expenses of the incineration furnace is large.

Therefore, the installation of such a typical incineration furnaceresults in an increased production expenses due to its highly increasedexpenses for the antipollution measures thereby requiring thedevelopment of an economical treatment system for waste water atlow-energy consumption.

Typically, in the incineration system, the organic waste water isdirectly sprayed into a high temperature of the furnace so as toevaporate the waste water in the furnace, and oxidize the gaseousorganic compounds. In case that the waste water includes salt, aquenching type incineration furnace as shown in FIG. 4 is employed, andin case of the waste water without salt, the heat exchangeableincineration furnace as shown in FIG. 5 is employed.

However, in the typical incineration method as described above, thewaste water is all directly sprayed into the furnace so that heat energyis oversupplied thereinto, and because of the use of just recovery heatexchanger, the heat recovery rate is very low with absence of medium forheat exchange.

SUMMARY OF THE INVENTION

The present invention provides an incineration system for treatingorganic waste water and volatile organic compounds while providing thesame efficiency with that of the incineration systems of related arts orbetter and saving the operation expenses for the system by at least 80%.

The main ideas and objects of the present invention can be summarized asfollows in three points.

First, a regenerative thermal oxidizer (now herein after referred to asRTO) for use in treating waste gas including organic compounds isemployed for treating waste water and an evaporator is employed forgenerating waste gas for the above purpose.

Second, heat energy created from the oxidation of the organic compoundsin the waste gas can be fed back to be used as a source to operate theevaporator while maximizing the characteristics of the RTO consuming alittle energy for the oxidation.

Third, the remnant not-treated gas present from the former stagegenerated during the switching of the operation of forward/rearwarddirection is accumulated at a certain space before being treated withbatch-processing at a later stage.

According to one aspect of the present invention, there is provided anincineration method for incinerating waste gas in the RTO afterevaporating the organic waste water including organic compounds byheating up to a certain temperature using an evaporator.

According to another aspect of the present invention, there is providedan evaporative and regenerative incineration system for organic wastewater in which waste gas is generated by evaporating organic waste waterincluding organic compounds, the generated waste gas is oxidized withair, and the heat energy from the oxidization is regenerated toevaporate the waste water.

It is to be understood that both the foregoing general description andfollowing detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 shows the operation state in a 2-bed RTO in the forwarddirection;

FIG. 2 shows the operation state in the rearward direction in the FIG.1;

FIG. 3 is a configuration showing a typical 2-bed type RTO using a gasbuffer;

FIG. 4 shows a typical incinerator for waste water including salt;

FIG. 5 shows a typical incinerator for waste water without salt; and

FIG. 6 shows an incineration system for organic waste water according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiment of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 6 is a configuration showing an evaporative and regenerative wastewater incineration system according to the present invention.

As illustrated in the drawing, there are a typical 2-bed typeregenerative thermal incineration system and a specially-designed bufferand an evaporator coupled each other. In other words, there is anevaporator 15 at the front of a regenerative thermal oxidizer(RTO) 18 ina typical regenerative thermal incineration system so as to heat andevaporate waste water before being introduced into the incinerationsystem.

An evaporative and regenerative waste water incineration system forwaste water according to the present invention will be described indetail referring to FIG. 6.

First, not-treated waste water is heated through a thermal exchanger 14and introduced into the evaporator 15. Waste gas is evaporated from thewaste water introduced into the evaporator 15, and the evaporated wastegas is mixed with not-treated gas, which was stored in a buffer 25 andthen, has been preheated passing through a buffer condenser 16 and athermal exchanger 17, which will be explained in the following, and themixed gas is introduced into the 2-bed type RTO 18. The condensed wastewater generated at this stage is fed back into a waste water tank.

In case that the waste gas is introduced into a left-side ceramic layer19 in the forward operation direction, c and b of a 3-way valve 21 areopened, and its a is closed.

The mixed gas introduced into the left-side ceramic layer 19 is heatedaround a temperature of 850° C., and the organic compounds are oxidizedwith temperature increased so that the temperature of the gas inside afurnace is maintained at a temperature of 950° C.

The heated oxidized gas is cooled down passing through a right-sideceramic layer 20, and then, is absorbed into a blower 23 through a 3-wayvalve 22, which opens its b and a and closes its c at this stage.

The forward direction operation as above is maintained for about 2minutes, and the rearward direction operation is, in turn, maintainedfor about 2 minutes by converting the gas flow path.

That is, the mixed gas is introduced into the right-side ceramic layer20 according to the rearward operation direction and c and b of the3-way valve 22 are open and its a is closed at this stage.

The mixed waste gas introduced into the right-side ceramic layer 20 isheated up to a temperature of 850° C. by a ceramic which is preheatedwith accumulated heat energy at the former stage, and the organiccompounds are oxidized with temperature increased so that thetemperature of the gas inside a furnace is maintained at a temperatureof 950° C.

The heated oxidized gas is cooled down passing through the left-sideceramic layer 19, and then, is absorbed into the blower 23 through the3-way valve 21 so as to be discharged into the air. At this stage, b anda of the 3-way valve 21 are open and its c is closed.

During the operation switching of the above forward and rearwarddirection, there becomes present not-treated gas at the front positionof the ceramic layer 19, 20 to introduce the above mixed waste gas. Theremnant not-treated waste gas is stored in the buffer during theoperation switching of the forward and rearward direction, which will bedescribed in detail.

First, assuming that the forward direction of operation is finished, band c of the 3-way valve 22 are open and its a is closed, and the b anda of the 3-way valve 21 are open and its c is closed for the start ofthe operation of the rearward direction.

At this stage, the blower 23 absorbs the above remnant not-treated gas,and when b and c of a 3-way valve 24 are open and its a is closed, theabove gas is stored in the buffer 25 through the buffer condenser 16made of ceramic. The not-treated gas at a high temperature is cooleddown while passing through the buffer condenser 16 of the ceramic, andthe volume of the above gas is reduced due to the cooling so as todecrease the size of the buffer 25.

The buffer 25 is in flow communication with the atmosphere, and storesnot-treated gas to be introduced during the predetermined switching timeowing to its volume corresponding to the switching time. While thenot-treated gas is stored in the buffer 25, the air introduced into thebuffer 25 at the former stage is discharged out of the buffer. While thenot-treated gas is discharged out of the buffer 25, the air isintroduced into the buffer from the atmosphere.

As described above, with the start of the operation of rearwarddirection, the waste gas discharged from the evaporator 15 is mixed withthe not-treated gas, which has been stored in the buffer 25, afterpassing through the buffer condenser 16 and being preheated in the heatexchanger 17. Here, the buffer condenser 16 is heated by taking out heatenergy from the introduced not-treated gas, and thus, the not-treatedgas is preheated passing through the buffer condenser 16.

According to the present invention, the RTO 18 consumes only smallamount of heat energy for its operation. Accordingly, only some amountof heat energy from the oxidation of the organic compounds in theintroduced mixed waste gas is used, and the rest of the heat energy issupplied to the evaporator 15 or other heat sources through a dischargeline P for surplus energy. Therefore, throughout the whole operations inthe system, the heat energy can be efficiently used.

This will be described in more detail in the following.

With the recovery rate of the calory by the exothermic reaction of theorganic compounds in the waste gas as 85%, the necessary calories forthe incineration of the waste gas and the evaporation of the waste waterinside the RTO are calculated. If the waste water including the organiccompounds is 2 MT (water 1950 kg and the waste organic compounds 50 kg),the amount of the air required for the incineration of the evaporatedwaste gas is determined as 1200 m³ with waste gas:air=1:1.

The calories required to evaporate the waste water is 1,950 kg×540kcal/kg=1,053,000 kcal. At this stage, the latent heat of the vapor is540 kcal/kg. If calculating calories necessary to incinerate in the RTO,and assuming the sum of the waste gas and air=2400 m³, CP=0.38, and thetemperature difference T between the inlet and the outlet=50° C., thecalories is 2400 m^(3×0.38) cal/m³° C.×50° C.=45,600 kcal. Therefore,the calories to evaporate the waste water and to incinerate the wastegas is

1,053,000 kcal+45,600 kcal=1,098,600 kcal  (1)

If the exothermic energy of the organic compounds in the waste gas is500,000 kcal/MT, the total energy is 500,000 kcal/MT 2 MT=1,000,000kcal. As described above, if the recovery rate is 85%, the totalcalories for the evaporation and the incineration is

1000,000 kcal×0.85 kcal=850,000 kcal.  (2)

Therefore, the calory to be supplied from the outside can be calculatedby subtracting (2) from (1). That is, 1,098,600 kcal−850,000kcal=248,600 kcal/2 MT=124,300 kcal/MT.

Meanwhile, the calory required in a typical incineration system iscalculated as follows:

In the typical incineration method, the waste water including theorganic compounds is heated for incineration. For this purpose, itshould be heated up to 950° C. to evaporate the water in the waste waterand to oxidize the organic compounds. If calculating the amount of thenecessary air, in case of 120% of air (compatible surplus air rate), forexample, it is 12.5 m³ with LNG of 1 m³ (10,000 kcal).

Therefore, when the temperature of the air to be introduced into theincineration system is 30° C., the calories necessary to increase thetemperature of the air (12.5 m³) up to 950° C. is 12.5 m³×0.35 kcal/m³°C.×(950° C.−30° C.)=4,000 kcal. The 4,000 kcal is a calory to increasethe temperature of the air, itself up to a temperature of 950° C., andthe calory to be used to evaporate is 6,000 kcal from the 10,000 kcal.

Alternatively, in case of 2 MT of the waste water including organiccompound (water 1950 kg, organic compound 50 kg), the calory requiredfor the evaporation is 1950 kg×900 kcal=1,755,000 kcal, and the totalsupply calory is 1,750,000 kcal×10,000 kcal(gross). 6,000kcal(net)=2,925,000 kcal. Besides the calory by the exothermic reaction,500,000 kcal/MT×2MT=1,000,000 kcal, the calory to be supplied from theoutside is 2,925,000−1,000,000=1,925,000 kcal. If the recovery rate ofthe heat energy in the waste heat recovery is 50%, the real calory to beused is 1,925,000 kcal×0.5=962,500 kcal/2 MT=481,250 kcal/MT. Therefore,the required unit calory rate is higher than the case of the presentinvention by about 3.9 times.

That is, according to the system for incinerating the organic wastewater of the present invention, the required calory can be saved by356,950 kcal for 1 MT compared with the typical incineration system.

As described above, according to the present invention, the installationexpenses for the system is lower than that of the typical one, and theoperation expenses can be saved by 80%.

In addition, while the waste water is directly introduced into anincinerator in the typical system, and is heated up to 950° C.,according to the present invention, since the waste water is evaporatedand then, mixed with the air before being supplied into RTO, the energyonly to evaporate before being introduced into RTO can be supplied fromthe outside, and the rest of the energy for the operation can berecovered by over 95%.

In addition, since the RTO consumes only small amount of energy due toits operational characteristics, that is, a portion of the energy fromthe oxidation of the organic compounds in the mixed waste gas is used,and the rest of the energy is supplied to the evaporator, the efficiencyof the heat energy is high throughout the whole system.

It will be apparent to those those skilled in the art that variousmodifications and variations of the present invention can be madewithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claim is:
 1. An incineration method of treating organic wastewater comprising the steps of: heating organic waste water up to acertain temperature to generate a waste gas in an evaporator;introducing the waste gas into a regenerative thermal oxidizer;oxidizing the waste gas with air; supplying a portion of heat energygenerated during the oxidizing into the evaporator; and discharging theoxidized gas from the regenerative thermal oxidizer.
 2. The incinerationmethod of treating organic waste water of claim 1, further comprisingpreheating the organic waste water before the heating.
 3. Theincineration method of treating organic waste water of claim 1, furthercomprising mixing the waste gas with an untreated waste gas which hasremained in a previous stage.
 4. The incineration method of treatingorganic waste water of claim 1, further comprising temporarily storingan untreated waste gas remaining the regenerative thermal oxidizer in abuffer.
 5. The incineration method of treating organic waste water ofclaim 4, further comprising cooling down the untreated gas before thestoring by passing through a buffer condenser.
 6. The incinerationmethod of treating organic waste water of claim 4, further comprisingheating the untreated gas stored in the buffer by passing through abuffer condenser.
 7. The incineration method of treating organic wastewater of the claim 1, wherein the regenerative thermal oxidizer is a2-bed type regenerative thermal oxidizer.
 8. An incineration system oftreating organic waste water comprising: an evaporator for heatingorganic waste water including organic compounds and generating a wastegas; a regenerative thermal oxidizer having a pair of ceramic layers,and a furnace, displaced between the pair of ceramic layers, wherein thewaste gas is introduced through one of the ceramic layer, preheated,oxidized with air in the furnace, and discharged through the other oneof the ceramic layers; and a blower for discharging the discharged gasfrom the regenerative thermal oxidizer.
 9. The incineration system oftreating organic waste water of claim 8, further comprising a firstvalve and a second valve for defining a first path to receive the wastegas from the evaporator and a second path to receive the waste gasdischarged from the regenerative thermal oxidizer according to andoperation of forward/rearward direction of the regenerative thermaloxidizer at the same time.
 10. The incineration system of treatingorganic waste water of claim 9, further comprising a buffer fortemporarily storing a untreated waste gas, which has remained at aprevious stage during a switching of the operation of theforward/rearward direction of the regenerative thermal oxidizer, until anext stage.
 11. The incineration system of treating organic waste waterof claim 10, further comprising a 3-way valve for switching a third pathto discharge treated waste gas from the regenerative thermal oxidizerand a fourth path to send the untreated gas into the buffer.
 12. Theincineration system of treating organic waste water of claim 10, whereina buffer condenser is installed before the buffer to perform heatexchange with the untreated waste gas.
 13. The incineration system oftreating organic waste water of a claim 8, further comprising a meansfor supplying the heat energy generated from the waste gas oxidized inthe furnace of the regenerative thermal oxidizer into the evaporator.14. The incineration system of treating organic waste water of claim 12,wherein the buffer condenser includes a ceramic.